Discussion Topic Posted for the NANOTUBE-99 Workshop:

There is reported evidence that some reversibly intercalated alkali metal bundles of SWNT may suffer structural damage in this process. The density of damaged sites may adversely impact intercalated versions of SWNT that are hoped to become superconducting:
Synthesis and structure of pristine and alkali-metal-intercalated single-walled carbon nanotubes, C. Bower, S. Suzuki, O. Zhou, Appl. Phys. A (1998) Vol. 67, 47-52.

Fixed interatomic distances seem to be important to the nature of quantum transport that leads to superconductive transitions. Perhaps some insight as to why nanotubes are not yet superconducting may come from an analysis of the microstructural evolution during the intercalation process. How do species intercalate SWNT bundles? It appears from the reversible intercalation of charged iodine chains into carbon nanotube ropes reported by L. Grigorian et al, Phys. Rev. Lett. Vol. 80, No.25, 5560-5563 that at least this intercalation involves structural disorder with voids along the channel length. Experimental analysis of the intercalation mechanism would be difficult, since the high conductivity of SWNT would not lend itself to maintain a TSD depolarization current, for example, to test for a desired cooperative relaxation. Some kind of nanoscale- DMA test setup, perhaps by assistance of STM or AFM might probe mechanical loss sensitivity to measure weak cooperative interactions of relaxing species during the intercalation process. In any case, some method to measure relative ability to keep ordered interatomic distances along the tube axis needs to be measured to assist this search. If it were somehow possible to induce a high degree of one dimensional intercalated ordering by some mechanism, then the sought superconductive transition, if it exists, might have a better chance of being observed.

Our fundamental understanding of the low temperature physics of any of the fullerene systems might be tested by a response to various hydrogen doping levels to changes in the current voltage characteristic, as well as the presence or absence of low temperature cooperative relaxation. Minimal expected intra-bundle SWNT intercalation damage is expected for hydrogen intercalation. Hydrogen is most likely to permit access to inner nanotube voids. Even if by negative example, hydrogen intercalated bundles of SWNT may prove to be our simplest test case to examine for effects that relate to nanotube superconductivity.

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